During the formation of semiconductor devices, it is often necessary to electrically couple layers which are vertically arranged. That is, it is often necessary to electrically couple features on one layer to features on an underlying or an overlying layer. In order to accomplish such a task, an opening is typically formed extending through the vertically arranged layers. The contact opening is then filled with a conductive material so as to form a conductive path extending between the vertically arranged layers.
Prior Art FIG. 1A shows a side sectional view of a step during a conventional contact etch formation method. In Prior Art FIG. 1A, a substrate, not shown, has a nitride layer 100 disposed thereover. An oxide layer 102 is disposed overlying the nitride layer 100. A photoresist layer 104 is disposed above oxide layer 102. In the conventional contact opening formation step illustrated in Prior Art FIG. 1A, photoresist layer 104 has been patterned to remove the photoresist from area 106. An opening (i.e. a portion of a contact opening) has then been formed extending through oxide layer 102 to the top surface of nitride layer 100.
Referring now to Prior Art FIG. 1B, after the formation of the opening extending to the top surface of nitride layer 100, nitride layer 100 is etched away to provide a contact opening at area 106. As shown in Prior Art FIG. 1B, the contact opening extends completely through both oxide layer 102 and nitride layer 100. In such an example, the formation of the contact opening is sometimes used in conjunction with a self-aligned contact etch.
As shown in Prior Art FIG. 1C, such a conventional contact opening formation method then removes the photoresist layer 104 of Prior Art FIGS. 1A and 1B. However, such a conventional contact opening does not have an ideal profile for subsequent semiconductor processing steps. Specifically, in such a conventional contact opening formation method, the upper edge of the contact opening is a sharp corner. For example, regions 108a and 108b of the contact opening are sharp corners. Such a profile induces preferential deposition of metal near the top of the contact during PVD processing. This cusping at the top of the contact results in inadequate filling at the bottom or void formation which reduces electrical performance and reliability of manufactured semiconductor devices.
Thus, a need exists for a method for forming a contact opening wherein the method provides for selective etching of a desired material. A further need exists for a method for forming a contact opening wherein the method does not required substantial deviation from existing semiconductor manufacturing steps and processes. Still another need exists for a method for forming a contact opening wherein the upper edge of the contact opening is beneficially shaped for subsequent processing.